In North Dakota, energy companies are using horizontal drilling and hydraulic fracturing to tap oil in a layer called the Bakken. Take a look at how it works.

1. North Dakota's Bakken Formation is a layer of dense, oil-bearing rock found at a depth of about 2 miles. To tap it, oil companies drill to the hydrocarbon-rich stratum, then curve the well bore 90 degrees so that it runs horizontally through the thin, irregular formation.

3. In multistage fracking, engineers perforate short segments of the production casing independently. This allows them to concentrate the hydraulic assault, creating longer cracks that allow more oil to flow to the well.

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